The present invention relates to a vehicle steering system which can perform an automatic steering control and cancel the control.
There are proposed techniques for performing an automatic steering of a vehicle by making use of a steering actuator provided on the vehicle. For example, a power steering system installed on a vehicle includes an electric motor or a hydraulic actuator as a steering actuator for imparting a steering force (a steering assist force) to a steering mechanism. Then, steered road wheels of the vehicle can be turned by controlling the output of the steering actuator without involving the manipulation of a steering wheel by the driver.
More specifically, in an automatic parking assist control, a target traveling path from a current position to a parking position of the vehicle is calculated, and a relationship of a target turning angle with a traveling distance of the vehicle is obtained so that the vehicle is reversed along the target traveling path so calculated. Then, the steering actuator is controlled based on a steering angle command value which is determined so as to attain a target turning angle according to a traveling distance of the vehicle. At this time, the driver only has to perform the adjustment of stopping position as well as the adjustment of vehicle speed by controlling the brake and accelerator pedals and does not have to manipulate the steering wheel.
During the automatic steering control is in effect, in the case that the driver finds an obstacle when the driver carefully looks at conditions in a traveling direction and on the periphery of the vehicle, the driver is required to apply the brake as soon as possible to stop the vehicle. To this end, in the related art described in JP-H10-114272A, an automatic parking control is designed to be implemented by making use of a creeping force of a vehicle equipped with an automatic transmission only when the brake are applied. Consequently, when finding an obstacle, the driver can manipulate a brake application device as soon as possible so as to stop the vehicle. In addition, when the driver gives up parking the vehicle during automatic parking control and starts the vehicle, the automatic parking control is designed to be cancelled by stopping the manipulation of the brake application device.
However, in the case that the driver stops manipulating the brake application device in order to cancel the automatic parking control after the driver found the obstacle in the traveling direction of the vehicle and has stopped the vehicle, there exists a fear that the vehicle continues to move towards the obstacle due to the creeping force and then eventually comes into contact with the obstacle. In addition, since the automatic parking control has not yet been cancelled in such a state that the vehicle is stopped while keeping the brake application device manipulated, when the driver attempts to avoid the obstacle by manipulating the steering wheel, the steering force inputted by the driver and the torque generated as a result of the automatic parking control are caused to interfere with each other. Because of this, the driver cannot smoothly move on to a subsequent driving operation after the driver has stopped the vehicle.
On the other hand, an automatic steering control system is disclosed in JP2998864B in which automatic steering is cancelled when the application of the brake is detected. However, the system cannot be applied to the automatic parking control in which the application of the brake is inevitable. Namely, if the system disclosed in JP2998864B is applied to the automatic parking control, the automatic parking control is cancelled without any delay by the application of the brake by the driver. Thus, the driver has to perform again the automatic parking mode setting operation or parking position setting operation. Consequently, once the brake is applied, the operation process for resuming the cancelled automatic parking control becomes complicated and troublesome. Therefore, the disclosed system cannot be put into practical use for the automatic parking control.
In this way, the conventional automatic steering function such as the automatic parking has the drawback that the driver cannot smoothly move on to a driving operation subsequent to the application of the brake, and this function is not necessarily easy for the driver to use.